Project I - Zhang & Chen Program Director/Principal Investigator (Last, First, Middle): Lipton, Stuart A. PROJECT SUMMARY (See instructions): The N-methyl-D-aspartate subtype of gluatmate receptor (NMDAR) is essential for normal function of the central nervous system (CNS). However, excessive activation of NMDARs, particulariy of extrasynaptic as opposed to synaptic receptors, mediates, at least in part, neuronal or synaptic damage in many neurological disorders, such as hypoxic-ischemic brain injury and, as recently suggested, in Down syndrome. Blockade of excessive NMDAR activity must be achieved without interference with its normal brain function. We have taken two approaches for clinically-tolerated pharmacological and genetic intervention on NMDARs. One approach is to use Memantine but also NO species to further down regulate the NMDAR by S-nitrosylation. The structural determinants on NMDARs for the action of Memantine and NO-like species will be characterized further under the auspices of this grant. Another approach is to utilize the inhibitory effect of a novel family of NMDAR subunits, composed of NRSA and NRSB, to downregulate NMDARs by affecting channel permeability, in a sense mimicking the effect of the NMDAR antagonist drugs that are also being developed here. We will study the role of the MS domain of NRS subunits that downregulate activity of NMDARs and also design NRS ligand-binding domain (LBD)-based screening assays to discover new compounds that modulate NRS-containing receptors. These agents will be useful for characterizing NRS-containing receptors, and possibly for neuroprotection. Accordingly, the Specific Aims of this proposal are as follows: 1) To study the effect of S-nitrosylation/redox modulation of the loose linker region between the amino-terminal domain (ATD) and the LBD of NMDARs by electrophysiology; 2) To develop LBD-derived screening assays to screen for ligands selective for the NRS subunit of the NMDAR. These ligands will be further characterized and refined by secondary assays, chemical modification, and co-crystallization; 3) To study the inhibitory effect of peptides derived from the out vestibule (MS) region of NRS subunits on NMDAR permeability.